Question:
Describe the 2 hypotheses (1-2 paragraphs)
o Describe hypothesis #1 (e.g., The X hypothesis (ref) proposes sleep loss…etc.)
o Describe hypothesis #2
o Make sure you highlight the similarities/differences between the 2 hypotheses
– Critically evaluate the empirical evidence for the 2 hypotheses (4-5 paragraphs)
o Start with a linking sentence – e.g., A number of studies have been conducted to test the two hypotheses.
o Then, describe how each paper supports or does not support each hypothesis. E.g., In an early study by [authors], participants were asked to…etc. (describe the research methodology briefly and summarise the findings, and make it clear which hypothesis it supports)
o Make sure you also identify any limitations/issues with each study
Answer:
There are several hypothesis postulated in order to ascertain the affect of sleep deprivation on the degree of mental alertness. This essay discusses on the two most important hypothesis postulated in the domain of sleep deprivation and tries to finds the significance of those two hypotheses under the light of the six different research papers conducted under the similar domain.
Hypothesis 1: Sustained Attention Performance During Sleep Deprivation: Evidence of State Instability
According to the hypothesis postulated by Doran, Dongen, Dinges, sleep deprivation in humans did not eradicate the strength to deliver neurobehavioral functions but on contrary it creates a imbalance in the state to alertness of the sleep deprived individual, preventing him or her in maintain stable pr alert performance for more than a minute. Sleep deprivation has significant affect on the performance variability and it is expressed as intermittent lapsing. This sleep deprivation affects the causes a state if instability along with as escalating homeostatic drive for sleep, uncontrolled initiation of sleep and strong resistance to prevent sleep by using compensatory effort. This state of instability affects the neurobehavioral performance. This imbalance in the neurobehavioral performance causes moment to moment divergence from attention with is associated with the homeostatic drive for sleep and circadian promotion of wakefulness. The Psychomotor Vigilance Test (PVT) Using done via implementing 88 hours of sleep deprivation was conducted in order to prove this hypothesis. The obtained results showed that the controlled group who was allowed to take 2 hours of NAP after every 12 hours (88 hours total) performed better in the PVT. Moreover, the results also showed that the performance variability of those who were kept awake for more than 18 hours at a stretch, declines rapidly accompanied with lack of motivation (Doran et al., 2001).
However, the hypothesis claims that the state of instability does not eliminate the sustained neurobehavioral responses. It only hampers or decelerates specific neurobehavioral functions like alertness, problem solving skills, psychomotor skills while promoting false responding. A sleep deprived person is able to perform short term task with alertness but when the difficulty and the duration of the task increases then the sleep deprived persons faces problems and this problem increases with the tenure of the sleep deprivation (Doran et al., 2001).
Hypothesis 2: Prefrontal Neuropsychological Effects of Sleep Deprivation in Young Adults—a Model for Healthy Aging
The prefrontal complex is the portion of the brain which is mainly responsible for a variety of different complex behaviors which includes planning as well as contributes to personal development. This is located in the front of the frontal lobe of the brain. Authors have found integral link between a people will to live along with their personality development and that of the functions of prefrontal cortex. They also contribute to decision making and moderating social behaviour. However, authors have developed a hypothesis which states that sleep deprivation in young adults results in impairment of the prefrontal cortex which is very similar to that of the preferential impairment that occurs in old age people during the time of their healthy aging. Authors are of the opinion that young people who suffer from sleep deprivation results in changes of the prefrontal complex in a pattern which is very similar to the modification that occur naturally in the prefrontal region of the brain in the old people. Therefore they have put forward a hypothesis that of they conduct research models by taking sleep deprived patients of the younger cohort, they would be able to study the normal process of aging of the brain of the old which would be beneficial for invention of new facts (Harrison, Horne & Rothwell, 2000).
Comparison of both the hypothesis:
Both the hypothesis reflects two different arenas of research. The first hypothesis mainly determines the activity of the prefrontal cortex in the sleep deprived young people. This hypothesis mainly talk about choosing the model of alterations occurring in the brain of sleep deprived young individuals which according to the authors are comparable to the alteration that take place during healthy aging of the old people. On the other hypothesize, authors mainly stressed on the performance level of individuals working in asleep deprived condition. In this hypothesis , authors state that long sleep deprived individuals are seen o provide forced compensatory effort which help them to accomplish short time tasks but they fail to provide concentration and attention when they are asked to complete in long sustained task which requires continuous attention. If the individuals are provided naps in between, the lapses frequency reduces resulting in better concentration. Otherwise the individuals who are sleep deprived will have frequent sleep attacks as well as lapses which will ultimately result the individual to go into uncontrollable sleep which eliminate wakefulness itself in the individual.
A number of studies have been conducted so far in order to ascertain the basis of these two above-mentioned hypotheses. The current essay sheds light on how these two above-mentioned hypotheses hold true or deviated in the actual case scenarios. The comparison or the relatedness of these hypotheses is done via analysing 6 research papers which are framed ‘specifically to ascertain the significance of these two hypotheses.
“Increasing Task Difficulty Facilitates the Cerebral Compensatory Response to Total Sleep Deprivation” this study was conducted by Sean and this group of researchers in the year of 2004. Their aim of the study is to analyse the affect of task difficulty on the cerebral compensatory response of total sleep deprived people. Here the participants where were asked to perform the modified version of the Baddeley’s Logical reasoning task while their are monitored via the magnetic resonance imagining. They were monitored twice, once after the normal tenure of sleep and once after 35 long hours of total sleep deprivation. The task was also simultaneously modified in order to parametrically manipulate the level of task difficulty. The participants were young (age mean: 27.6 +/- 6.1 years). The results showed that the degree of task difficulty facilitates the cerebral compensatory response during the tenure of total sleep deprivation. This compensatory response was found to express in new in new regions of the brain that otherwise has no relation with the “task demand” under the normal/well rested condition. Moreover, stronger compensatory responses are generated in the regions of the brain which are significantly related with the process of undergoing the task during well rested condition (Drummond et al., 2004). This study works in sync with the hypothesis 1 (sustained action performance), which states that a sleep deprived person is able to perform short term task with alertness via generating compensatory response in the brain (Doran et al., 2001).
The paper “Lapsing during Sleep Deprivation Is Associated with Distributed Changes in Brain Activation” has been authored by researchers Chee et al., in the year 2008. Twenty four right handled male and female patients were allocated for the experiment out of which 17 subjects were ultimately incorporated to the experiential setting. They visited the laboratory three times each time with predefined activities. After the conducting of the activities and tests taken by researchers it was found that sleep depression resulted in slower as well as less accurate and more variable performance and also affected different task related activity performance. Lapses were also found to be associated with reduction of virtual and cortical activities in SD patients. The researchers performed functional magnetic resonance imaging during visual as well as selective attention task and mainly noticed the correct responses in a trial by trail pattern and then modelled the effects of the response. When comparison are done between sleep deprived individuals and individuals taking normal night sleep, it was found that lapses differ as the previous had reduced ability of the frontal and parietal region to raise activation to respond to the lapses, resulted in reduction of activation of visual sensory cortex and reduced thalamic activation during lapses in comparison to elevated activation in non lapse period (Chee et al., 2008). This theory has inculcate the mixing of both the hypothesis as the authors have used the prefrontal characteristic changes in sleep deprived patients like the first hypothesis and showed their effect on the brain function and normal activity level of the participants in regular tasks like the second hypothesis.
Chee and Choo conducted experiments and published their work through the Functional Imaging of Working Memory after 24 Hr of Total Sleep Deprivation which was published in the year 2004. The authors had mainly incorporated 14 participants who were young and were right handed. The main motive of the study was to analyze the neurobehavioral effects after 24 hour of sleep in those young adults. Before conducting magnetic resonance imaging, they were allowed to go through two tests (LTS and PLUS) – one with testing maintenance in four blocks and the other in manipulation and maintenance in three blocks. Response time after sleep deprivation in both the tasks was slower. An interesting observation was found here. Different patterns of changes occurred in the different portion of the parietal frontal portions of the brain which result in cognitive impairment of the brain regions after sleep deprivation. However, increased prefrontal and thalamic activation helps the participants to undertake compensatory adaptation. All the finding of the papers help the researchers to come to a conclusion that more complex tasks are well done by sleep deprived individuals than simple tasks. This is based on the first hypothesis as researchers have mainly discussed about the brain regions related functional modifications and have also stated that this model matches with occurrences of changes of the elder adults (Chee & Choo, 2004).
Drummond et al. had published a paper “Sleep deprivation-induced reduction in cortical functional response to serial subtraction” in the year 1999. They had the main aim of studying the effects of sleep deprivation on the different functional alteration in the brain and thereby to study these changes. For these, they had taken thirteen normal healthy subjects after taking their written consents. They were made to perform 4 different tasks twice a day and at the same time fMRI scans were done – once after a normal night sleep and one after a sleep deprived sleep. Arithmetic tasks were mainly conducted. The authors wanted to know that whether the prefrontal cortex and parietal lobe had any alterations due to the affects of SD. It was seen that in comparison to that after the normal night sleep, activities of the mentioned regions of the brain decreased after sleep deprivation especially in the PFC (Drummond et al., 1999). The work aligns with the first hypothesis as the main discussion remains concerned with the effects on the different parts of the brain and their related functional decrease or functional loss.
The study, “The Neural Basis of Psychomotor Vigilance Test” was conducted Drummond with the group of researchers in the year of 2005. The aim of the study is to identify the regions of the brains that promote fastest and slowest reaction times during the Psychomotor Vigilance Test (PVT). The study was conducted under well-rested conditions and is particularly directed towards the specific regions of the brain, which deliver extremely poor performance during the tenure of sleep deprivation. The study was conducted with 20 right handed healthy adults (age mean: 27.4 +/- 6.7 years) who were made to undergo two PVTs and while they are giving PVT, their brains were analysed under magnetic resonance imaging. These two PVT tests were performed after every 12 hours (after waking up from a normal night sleep) and after 36 hours of total sleep deprivation. The results obtained showed that optimal performance of the brain during the PVT test depends on the activation of both sustained attention system and motor system. The poor performance following the PVT, recorded after the total sleep deprivation is the result of the poor attention. However, in order to make up the poor performance, brain at times elicit compensatory response to that particular positions of the brain that are responsible for fast and attentive performance. These findings are in accordance with the hypothesis 1 (sustained action performance) which states that the poor performance of the individuals in the PVT after TSD is a result of the decrease in the mental alertness or poor attention. The brain fails to stay alert after prolong hours of sleep deprivation and hence provides poor result in the PVT (Doran et al., 2001).
The aim of the study, “Neural basis of alertness and cognitive performance impairments during sleepiness. I. Effects of 24 h of sleep deprivation on waking human regional brain activity”, conducted by Thomas et al., in the year of 2000 was to analyse the significance of the hypothesis which states that the negative effects of the sleep deprivation on alertness and cognitive performance is a result of the decrease in the activity of the brain, mainly in the sub cortical region and prefrontal cortex. In order to conduct the study, Thomas et al., performed Positron Emission Tomography (PET) over 17 normal subjects who were sleep deprived for 85 hours. They used Fluorine 2-deoxyglucose (FDG) is a marker to detect the cerebral metabolic rate of the glucose (CMRglu) and simultaneous neuronal synaptic activity. 2 scans per subject was done per 24 hours intervals. The study showed short term sleep deprivation results in global decrease in the brain activity with significant decrease in the global CMRglu. This study works in sync with both the hypotheses. It proved the influence of prefrontal cortex on neuropsychological effects of the sleep deprivation and also indicated that how sleep deprivation cast a negative impact on the cognitive performance and alertness (Doran et al., 2001; Harrison, Horne & Rothwell, 2000).
Thus from the above discussion it can be concluded that the sleep deprivation has a prominent affect on the degree of alertness of the brain and is mostly concerned with the prefrontal cortex of the brain.
Reference List
Chee, M. W., & Choo, W. C. (2004). Functional imaging of working memory after 24 hr of total sleep deprivation. Journal of Neuroscience, 24(19), 4560-4567.
Chee, M. W., Tan, J. C., Zheng, H., Parimal, S., Weissman, D. H., Zagorodnov, V., & Dinges, D. F. (2008). Lapsing during sleep deprivation is associated with distributed changes in brain activation. Journal of Neuroscience, 28(21), 5519-5528.
Doran, S. M., Van Dongen, H. P. A., & Dinges, D. F. (2001). Sustained attention performance during sleep deprivation: evidence of state instability. Archives italiennes de biologie, 139(3), 253-267.
Drummond, S. P., Brown, G. G., Salamat, J. S., & Gillin, J. C. (2004). Increasing task difficulty facilitates the cerebral compensatory response to total sleep deprivation. Sleep, 27(3), 445-451.
Drummond, S. P., Brown, G. G., Stricker, J. L., Buxton, R. B., Wong, E. C., & Gillin, J. C. (1999). Sleep deprivation‐induced reduction in cortical functional response to serial subtraction. Neuroreport, 10(18), 3745-3748.
Harrison, Y., Horne, J. A., & Rothwell, A. (2000). Prefrontal neuropsychological effects of sleep deprivation in young adults–a model for healthy aging?. Sleep, 23(8), 1067-1073.
Sean P. A. Drummond, Amanda Bischoff-Grethe, David F. Dinges, Liat Ayalon, Sara C. Mednick, M. J., & Meloy. (2005). The Neural Basis of Psychomotor Vigilance Test. Sleep, 28(9), 1059-68.
Thomas, M., Sing, H., Belenky, G., Holcomb, H., Mayberg, H., Dannals, R., … & Welsh, A. (2000). Neural basis of alertness and cognitive performance impairments during sleepiness. I. Effects of 24 h of sleep deprivation on waking human regional brain activity. Journal of sleep research, 9(4), 335-352.
